SOI substrate compatible with the RFSOI and FDSOI technologies

ABSTRACT

A semiconductor on insulator type substrate, comprising at least:
         a support layer;   a semiconductor surface layer;   a buried dielectric layer located between the support layer and the semiconductor surface layer;   a trap rich layer located between the buried dielectric layer and the support layer, and comprising at least one polycrystalline semiconductor material and/or a phase change material;       

     in which the trap rich layer comprises at least one first region and at least one second region adjacent to each other in the plane of the trap rich layer, the material of the at least one first region being in an at least partially recrystallized state and having an electrical resistivity less than that of the material in the at least one second region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. Ser. No.16/003,199, filed on Jun. 8, 2018, which claims the benefit of priorityfrom French Application No. 1755314, filed on Jun. 13, 2017; thecontents of each of which are incorporated herein in their entirety.

TECHNICAL DOMAIN AND PRIOR ART

The invention relates to the field of RFSOI (Radio-Frequency Silicon OnInsulator) and FDSOI (Fully Depleted Silicon On Insulator) substrates,and semiconductor devices made from such substrates.

There are two distinct types of SOI substrates used for differentelectronic applications:

-   -   RFSOI substrates used for Radio Frequency (RF) applications as        Front End modules;    -   FDSOI substrates used for high performance low consumption        digital applications, and for the fabrication of FDSOI type        components.

These two types of SOI substrates have specific characteristics adaptedfor one of these two distinct applications.

Thus, an FDSOI substrate comprises a thin silicon surface layer (forexample 10 nm thick), a thin buried dielectric layer or BOX (for example20 nm thick), and a support layer or solid layer made of slightly dopedsilicon (for example with a resistivity of between about 0.1 and 1Ohm·cm) placed under the BOX to enable back polarisation of FDSOItransistors made in this substrate. Therefore mobility in the channel ofsuch an FDSOI transistor can be controlled from the back face of thesubstrate that forms a back gate of the transistor, due to a slightlyresistive lateral contact accessible from the front face of thesubstrate and that is connected to the portion of doped silicon locatedunder the BOX of the transistor. This back polarisation can be used tomodulate the performances (particularly the speed) and/or theconsumption of the transistors made, and particularly their thresholdvoltage. However, this requires good electrical conduction between thefront face contact and the doped zone formed under the BOX of thetransistor.

On the contrary, an RFSOI substrate comprises a highly resistive supportlayer (for example with a resistivity greater than or equal to about 0.5kΩ·cm, or even more than 1 kΩ·cm) to limit losses in RF or passivecomponents made on or in such a substrate.

A major problem that occurs for RF applications is the presence of aparasite conduction layer formed by parasite free charges generated bythe presence of fixed charges in the BOX of the substrate. This isparticularly damaging to the linearity of RF signals that account fornon-negligible powers (0 to 30 dBm), and causes crosstalk.

To solve this problem, it is possible to have a “trap rich” layer justunderneath the BOX to capture free charges and thus considerably reduceor even eliminate formation of the parasite conducting layer. This traprich layer is formed, typically by PECVD, LPCVD deposition or byepitaxy, on the support layer just before the RFSOI substratefabrication process. The RF components are then fabricated on the RFSOIsubstrate in the same way as on a classical SOI substrate.

Advantageously, the trap rich layer is formed by a deposit ofpolysilicon. Unlike other techniques, the polysilicon makes it possibleto achieve a high trap density, a high resistivity (between about 5 and10 kOhm·cm), and good thermal stability at high temperature (up to about1100° C.) compatible with the use of a CMOS process, while enabling thepossibility of depositing or growing a silicon oxide to passivate thelayer and thus make direct bonding of this oxide layer possible duringfabrication of this substrate. An example of a method of making an RFSOIsubstrate comprising a trap rich layer is described in document EP 1 665367 A1.

Document FR 2 973 158 A1 also describes a technique to stabilise thegrains in the trap rich layer by inserting a thin dielectric layerbetween the trap rich layer and the support layer to prevent or delayuntimely recrystallization of the trap rich layer that is responsiblefor the drop in efficiency of this layer.

In all cases, the trap rich layer of an RFSOI substrate is formeduniformly on the substrate and is designed to be thermally stable.

With the upcoming technologies (22 nm and smaller), and emergence of theIoT (Internet Of Things) and 5G (fifth generation of standards formobile telephony), it would be very interesting to have a highperformance SOI substrate for existing FDSOI type active devices andalso for passive devices and RF devices.

However, the presence of a highly resistive trap rich layer, useful forpassive or RF components, is incompatible with back polarisation ofFDSOI transistors and that requires conduction between the insulationzones and under the BOX so as to control the back gates of FSDOItransistors in voltage through the back face.

Furthermore, shaping of the trap rich layer that would consist offorming this layer only at locations to be used for RF or passivecomponents during fabrication of the SOI substrate is not industriallyfeasible because it would require the founder or the integrated circuitfabricator to give details and the drawing of circuits to be made to themanufacturer of the substrate that will be used for fabrication of theintegrated circuits.

PRESENTATION OF THE INVENTION

Thus there is a need to propose a new semiconductor on insulator typesubstrate with the advantages of an RFSOI substrate comprising a traprich layer, while being compatible with the FDSOI technology andparticularly with back polarisation of FDSOI components, andparticularly FDSOI transistors, made on this substrate.

To achieve this, it is proposed a semiconductor on insulator typesupport, comprising at least:

-   -   a support layer;    -   a semiconducting surface layer;    -   a buried dielectric layer located between the support layer and        the surface layer;    -   a trap rich layer located between the buried dielectric layer        and the support layer, and comprising at least one        polycrystalline semiconducting material and/or a phase change        material;

in which the trap rich layer comprises at least one first region and atleast one second region adjacent to each other in the plane of the traprich layer, the material of the first region being in an at leastpartially recrystallized state and having an electrical resistivity lessthan that of the material in the second region.

This substrate comprises a trap rich layer, the structure of which issuch that the benefits of an RFSOI structure can be associated with thebenefits of an FDSOI structure within a single substrate, through thefabrication of distinct regions within the trap rich layer, thesedistinct regions having different properties depending on whether theywill form part of an RFSOI region of the substrate or an FDSOI region ofthe substrate.

The use of a polycrystalline semiconductor and/or a phase changematerial to form the trap rich layer makes it possible to make a localadjustment of the properties of this layer, for example through the useof a laser, and thus to delimit different regions within this layerdepending on the FDSIO or RFSOI properties required for each region.

The majority of traps in the trap rich layer are formed at grainboundaries, where they are associated with pendant bonds of thematerial. Depletion regions and potential barriers are formed aroundgrains to compensate for charges trapped at grain boundaries. Thesurface area of grain boundaries must be maximised so as to increase thedensity of traps and consequently the efficiency of the trap rich layer,which implies that the grain size must be reduced. For example,polysilicon grains with a size of between about 100 nm and 150 nm can beused to obtain the nominal resistivity of silicon that is of the orderof 5 kOhm·cm.

The uniformity of the grain size, the columnar structure and themorphology of grains within the trap rich layer along its thickness havea strong influence on the efficiency at which parasite currents arereduced. The thickness of the trap rich layer also plays an importantrole.

Furthermore, the resistivity of the trap rich layer and its property ofreducing parasite conduction reduce with increasing grain size. Bylocally heating the first region(s) of the trap rich layer, the materialwithin this or these first regions recrystallizes, generating anincrease in the grain size of the material within this or these firstregions. This reduces the electrical resistivity of this recrystallizedmaterial and makes this or these regions adapted to the FDSOItechnology, while keeping the other region(s) of the substratecompatible with the RFSOI technology.

This local adjustment may correspond to significant heating of thematerial in the first region, modifying the structure of the grains fromwhich it is composed and lowering its resistivity.

The part of the substrate including the first region of the trap richlayer and the portions of other layers of the substrate located on thisfirst region form a part of the substrate adapted to the fabrication ofFDSOI components. The part including the second region of the trap richlayer and the portions of other layers of the substrate located on thissecond region form a part of the substrate adapted to the fabrication ofRF and/or passive components.

Therefore the substrate comprises a trap rich layer that can bedeactivated or modulated locally as a function of the requiredcharacteristics within the different regions of the substrate,particularly regions that will receive active zones of FDSOI components.The regions on which passive and/or RF components (inductor,transmission lines, etc.) will be made are located facing a functional“trap rich” region, i.e. a region in which the material in the trap richlayer is in a non-recrystallized state.

Therefore this substrate comprises highly resistive regions under theburied dielectric layer, without a parasite conduction zone at thelocation at which the trap rich layer is functional (non-recrystallizedmaterial), and regions that are less electrically resistive at thelocation at which the properties of the trap rich layer have beenmodified, so that back polarisation of active components made at theseregions becomes possible.

The material in the first region of the trap rich layer isrecrystallized such that the grain structure of this material ismodified (increase in the grain size) lowering the resistivity of thematerial in this first region. Recrystallization may be continued untilthe recrystallized material in the first region is monocrystalline.

Due to the lower electrical resistivity of the material in the firstregion of the trap rich layer, this material can be used to form a backpolarisation gate of FDSOI components made at this first region.

The plane of the trap rich layer corresponds to the principal plane ofthis layer that is parallel to the interfaces between the differentlayers of the substrate.

The trap rich layer may comprise at least one of the followingmaterials: polycrystalline silicon, polycrystalline germanium,polycrystalline silicon-germanium, phase change material.

The trap rich layer is advantageously sensitive in absorption tolighting (in other words capable of absorbing electrons from thislighting) making use of at least one wave length at which the materialof the support layer and/or the material of the surface layer istransparent, for example a wave length in the infrared range. This isthe case when polycrystalline germanium and/or polycrystalline SiGeand/or a phase change material is used to form the trap rich layer andsilicon is used to form the support layer and/or the surface layer, thelighting used emitting one or more wave lengths in the infrared range.

Advantageously, the melting temperature of the material in the surfacelayer is higher than the recrystallization temperature of the trap richlayer to give good selectivity of heating when the trap rich layer isheated through the surface layer. This is the case particularly when thesurface layer comprises monocrystalline silicon that has a high meltingtemperature (about 1415° C.) and the trap rich layer comprisespolycrystalline silicon (recrystallization temperature between about800° C. and 900° C.), polycrystalline Ge, polycrystalline SiGe, or aphase change material. This may also be applicable between the materialin the trap rich layer and the material in the support layer whenlighting takes place through the support layer.

A phase change material has the advantage that its crystalline state isreversible and it can quickly change from the crystalline state to theamorphous state, or vice versa.

A thickness of each of the grains in the material in the first regionmay be equal to or close to the thickness of the trap rich layer, whichcan give good electrical conductivity of the material in the firstregion.

The trap rich layer may comprise a phase change material that is in thecrystalline state in the first region and in the amorphous state in thesecond region.

The substrate may comprise a heat absorption layer located between thetrap rich layer and the support layer. In this case, the main functionof the heat absorption layer is to absorb radiation used to heat andrecrystallize the material in the first region of the trap rich layer.

In this case:

-   -   the trap rich layer may comprise polycrystalline silicon, and    -   the heat absorption layer may comprise polycrystalline germanium        or polycrystalline silicon-germanium or a phase change material.

When the heat absorption layer comprises polycrystalline germanium orpolycrystalline silicon-germanium or a phase change material, thematerial in this layer that receives the thermal radiation is also atleast partially recrystallized.

It is also proposed a semiconducting device comprising at least:

-   -   a substrate like that described above;    -   a first insulation trench passing through at least the surface        layer, the buried dielectric layer and the trap rich layer of        the substrate and separating the first and second regions in the        trap rich layer of the substrate from each other;    -   an FDSOI component made in a first portion of the surface layer        of the substrate that is superposed on the first region of the        trap rich layer of the substrate;    -   a passive and/or RF component made in and/or on a second portion        of the surface layer of the substrate that is superposed on the        second region of the trap rich layer of the substrate;

The device may also include:

-   -   a doped well formed in a portion of the substrate support layer        in contact with the first region of the trap rich layer of the        substrate;    -   a second insulation trench passing through at least the surface        layer, the buried dielectric layer and the trap rich layer of        the substrate and separating first and second parts of the first        region of the trap rich layer of the substrate that are        electrically connected to each other through the doped well, the        first part of the first region of the trap rich layer of the        substrate forming a back polarisation plane, or back gate, for        the FDSOI component;    -   an electric contact passing through the surface layer and the        buried dielectric layer, in contact with the second part of the        first region of the trap rich layer of the substrate.

The electric contact may be used to apply an electric potential on thefirst part of the first region of the trap rich layer through the dopedwell and the second part of the first region of the trap rich layer.

It is also proposed a method of fabricating a semiconductor on insulatortype substrate, including fabrication of a stack comprising:

-   -   a support layer;    -   a semiconducting surface layer;    -   a buried dielectric layer located between the support layer and        the surface layer;    -   a trap rich layer located between the buried dielectric layer        and the support layer, and comprising at least one        polycrystalline semiconducting material and/or a phase change        material;

and also comprising, in the trap rich layer, at least one first regionand at least one second region adjacent to each other in the plane ofthe trap rich layer, during which the material in the first region is atleast partially recrystallized such that its electrical resistivity lessthan that of the material in the second region.

Fabrication of the first region may include the use of local annealingof the material in the first region, by laser.

The laser emits light for which the wavelength is absorbed by the traprich layer. The effect of the laser is to achieve significant annealingclose to the melting temperature of the trap rich layer and increase thegrain size of this material. This increase in the grain size of thematerial in the trap rich layer reduces the trap density at theinterface with the buried dielectric layer. For example, this has theeffect of reducing or even destroying the electric charge trappingeffect at the location at which the FDSOI components will be fabricated,while also guaranteeing good resistivity and very good linearity inzones of the substrate dedicated to RF.

The surface layer of the substrate may comprise monocrystalline siliconand, during the local laser annealing of the material in the firstregion, the laser may be focussed on the first region of the trap richlayer through the surface layer and the buried dielectric layer of thesubstrate.

The wavelength of light emitted by the laser may be chosen such thatthis light is not absorbed by silicon in the surface layer, for examplein the infrared range.

As a variant, during local laser annealing of the material in the firstregion, the laser may be focussed on the first region of the trap richlayer through at least the support layer of the substrate.

In this case, the buried dielectric layer may act as a thermal barrierso that the surface layer is not heated.

According to another variant, the substrate may also comprise a heatabsorption layer arranged between the trap rich layer and the supportlayer, and the laser may be focussed on a region of the heat absorptionlayer superposed on the first region of the trap rich layer and throughat least the support layer of the substrate.

It is also proposed a method of fabricating a semiconducting devicecomprising at least:

-   -   the use of a method of fabrication of a semiconductor on        insulator type substrate like that described above;    -   fabrication of at least one first insulation trench between the        first and second regions of the trap rich layer of the        substrate, passing through at least the surface layer, the        buried dielectric layer and the trap rich layer of the        substrate;    -   fabrication of at least one FDSOI component made in a first        portion of the surface layer of the substrate that is superposed        on the first region of the trap rich layer of the substrate;    -   fabrication of at least one passive and/or RF component in        and/or on a second portion of the surface layer of the substrate        that is superposed on the second region of the trap rich layer        of the substrate.

In this method, the components (in other words the FDSOI component(s)and the passive and/or RF component(s)) may be made before or aftercreating the first and second regions in the trap rich layer. When thecomponents are made before the first and second regions of the trap richlayer are fabricated, the material in the first region(s) isrecrystallized (for example by exposure to laser radiation) through theback face of the substrate to avoid damaging the components.

The method may also include:

-   -   fabrication of a second insulation trench passing through at        least the surface layer, the buried dielectric layer and the        trap rich layer of the substrate, and separating the first and        second parts of the first region of the trap rich layer of the        substrate;    -   implantation of dopants in a portion of the support layer of the        substrate that is located in contact with the first region of        the trap rich layer of the substrate, forming a doped well        electrically connecting the first and second parts of the first        region of the trap rich layer of the substrate to each other;    -   fabrication of an electrical contact passing through the surface        layer and the buried dielectric layer, in contact with the        second part of the first region of the trap rich layer of the        substrate, allowing control of a back polarisation plane of the        FDSOI component formed by the first part of the first region of        the trap rich layer of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention will be better understood after reading the descriptionof example embodiments given purely for information and that are in noway limitative with reference to the appended drawings on which:

FIG. 1 shows a first embodiment of a semiconductor on insulator typesubstrate;

FIGS. 2A and 2B show the steps of a method of fabricating asemiconductor on insulator type substrate according to the firstembodiment;

FIGS. 3 and 4 show a second embodiment and a third embodimentrespectively of a semiconductor on insulator type substrate;

FIGS. 5A to 5D show the steps in a method of fabricating a semiconductordevice, comprising FDSOI components and RF and/or passive componentsfabricated on the same substrate.

Identical, similar or equivalent parts of the different figuresdescribed below have the same numeric references to facilitatecomparison between the different figures.

The different parts shown on the figures are not necessarily all at thesame scale, to make the figures more easily understandable.

It must be understood that the different possibilities (variants andembodiments) are not mutually exclusive and that they can be combinedwith each other.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

Refer firstly to FIG. 1 that diagrammatically shows a first embodimentof a semiconductor on insulator type substrate 100.

The substrate 100 comprises a support layer 102 that acts as amechanical support layer. This layer 102 comprises a material said to bea “high resistivity” material, in other words its electrical resistivityis more than about 0.5 kΩ·cm, and preferably more than about 1 kΩ·cm oreven more than about 3 kΩ·cm, so that this layer 102 is compatible withthe fabrication of passive and/or RF components, in other wordscompatible with the RFSOI technology. In the first embodiment describedherein, the layer 102 comprises silicon. For example, the electricalresistivity of this silicon is equal to about 5 kΩ·cm. The thickness ofthe layer 102 is equal to several hundred microns.

The substrate 100 also comprises a semiconducting surface layer 104.Electronic components will be made on and/or in this layer 104. In thefirst embodiment described herein, the layer 104 comprisesmonocrystalline silicon. Therefore the substrate 100 is a silicon oninsulator (50I) type substrate. The thickness of the layer 104 is forexample between about 10 nm and 20 nm.

The substrate 100 also comprises a buried dielectric layer 106, or BOX,located between the layers 102 and 104. For example, this layer 106comprises SiO₂ and its thickness is between about 10 nm and 100 nm, andadvantageously between about 10 nm and 25 nm.

The substrate 100 also comprises a trap rich layer 108, located betweenthe layers 102 and 106. The layer 108 is between about 200 nm and 500 nmthick.

In the first embodiment, the layer 108 comprises a polycrystallinesemiconducting material. This polycrystalline semiconductor may bepolycrystalline silicon, or polycrystalline germanium, orpolycrystalline SiGe.

The layer 108 is not homogeneous because it comprises at least one firstregion 110 and at least one second region 112 located side by side inthe plane of layer 108 (in other words side by side in a plane parallelto the (X,Y) plane shown on FIG. 1). Each of these regions 110, 112occupies the entire thickness of the layer 108, in other words itsthickness is equal to the thickness of the layer 108.

The first region(s) 110 comprise(s) the polycrystalline semiconductormentioned above but that has been subjected to an at least partialrecrystallization. The second region(s) 112 comprise(s) this samepolycrystalline semiconductor but on which this recrystallization stephas not been carried out. The electrical resistivity of the material inthe first regions 110 is less than the electrical resistivity of thematerial in the second regions 112.

Recrystallization that occurs on the material in the first region(s) 110increases the grain size of this material, reducing or eliminating thecapacity of the material in this or these first regions 110 to trapelectric charges and reducing the electrical resistivity of thismaterial. The thickness of the grains in the material in the layer 108in the first region(s) 110 is equal to the thickness of the layer 108.

As a variant to the first embodiment described above, the trap richlayer 108 may comprise a phase change material instead of apolycrystalline semiconducting material. In this case, this material isin the crystalline state in the first regions(s) 110 and in theamorphous state in the second region(s) 112.

Such a phase change material may for example by a material in thechalcogenides family, for example Ge_(x)Sb_(y)Te in which 0<X≤1, 0≤Y<1and X+Y=1. A phase change material may be deposited with classicalmicroelectronics tools for example by a PVD, PECVD deposition in theamorphous or crystalline phase and with a thickness of between about 100nm and several microns.

In the amorphous state, phase change materials have a very highresistivity, of the order of 1 MΩ·cm. In the crystalline state, thesematerials are electrically conducting and have a very low resistivity,of the order of a few mΩ·cm.

These phase change materials can reversibly change from the amorphousstate to the crystalline state depending on the profile (duration andintensity) of the annealing applied to them. The change from theamorphous state to the crystalline state usually takes place at betweenabout 500° C. and 700° C.

A method of fabricating the substrate 100 is described with reference toFIGS. 2A and 2B.

The first step is to fabricate a stack of layers 102, 108, 106 and 104,as shown on FIG. 2A. These layers can be formed by carrying out severalsuccessive deposition steps.

An at least partial recrystallization of the material in layer 108 isthen implemented at the part(s) of the layer 108 that will form thefirst region(s) 110. In this case, this recrystallization corresponds toa local annealing performed using a laser with a beam shown on FIG. 2Bwith reference 114. On the example in FIG. 2B, this annealing is appliedthrough a front face 116 of the substrate 100, in other words the laserbeam passes through the layers 104 and 106 before reaching the layer108. As a variant, the material in the first region(s) 110 may berecrystallized through a back face 118 of the substrate 100, the laserbeam 114 passing through the support layer 102 before reaching thematerial in the layer 108.

The laser used may be a pulsed laser, so that the power can be increasedlocally to reach the required temperatures for recrystallization of thematerial in the layer 108. The laser emission device used may forexample have the following properties:

-   -   wavelength: 1.035 μm,    -   output power: 40 W,    -   energy: 40 μJ (at 1 MHz),    -   frequency: 1 MHz,    -   beam diameter at 1 metre: 2.7 mm+/−0.3.

For example, in this case the laser is used such that the diameter ofthe input beam to the layers of the substrate 100 is between 0.5 mm and2 mm, so that a good resolution can be obtained between the regions 110,112. Advantageously, the wavelength of the laser beam used can bebetween about 1.3 μm and 1.4 μm, the difference in absorption of such awavelength by Ge and Si being very significant.

For example, a Ge layer 108 with a thickness equal to 200 nm locatedunder an SiO₂ layer 106 with a thickness equal to 25 nm and under a Silayer 104 with a thickness equal to 20 nm can reach a temperature ofabout 900° C., namely a temperature close to the melting point ofgermanium and making partial recrystallization of germanium in layer 108possible, using a 500 μJ laser pulse with a duration of 1.45 nsgenerated by the emission device described above. With such a laserpulse, the temperature of the layer 104 does not exceed 500° C., andtherefore does not alter the silicon in the layer 104, particularly dueto the thermal barrier formed by the layer 106 between the layers 104and 108.

In this first embodiment, the trap rich layer 108 has electric chargetrapping properties and is also sensitive to the laser used forrecrystallization of the material in the first regions 110.

Polycrystalline germanium has the advantage that it strongly absorbswavelengths in the infrared range (wavelength longer than about 1 μm).Thus, a laser emitting infrared light can be used to produce differentregions 110, 112 within the layer 108, these wavelengths not beingabsorbed or being only slightly absorbed by the silicon that can formthe layer 104. This is also the case when a phase change material isused to form the layer 108 and when the layer 104 contains silicon.

Furthermore, germanium has a direct gap, which facilitates absorption oflight excitation and a lower melting temperature than silicon, which isconducive to the phase change of the layer 108 when it comprisesgermanium.

However, the charge trapping effect obtained with polycrystallinegermanium is lower than when polycrystalline silicon is used.

Polycrystalline SiGe can thus be used in the layer 108 to stabilise thematerial, create conditions more suitable for growth of the material inlayer 108 and increase the resistivity of the final material obtained(in comparison with germanium).

Polycrystalline Ge and/or SiGe and/or Si can be deposited in existingPECVD, LPCVD type microelectronics or epitaxy frames.

As a variant to the method described above, it is possible to useseveral laser beams simultaneously focussed at the same point in layer108 to recrystallize the material in the first regions 110. Thus,heating of layer 104 is limited when these beams pass through the frontface 116 of the substrate 100 and when they pass through the differentportions of the layer 104. This variant can also be applied when thebeams enter the device 100 through the back face 118 formed by the layer102.

FIG. 3 shows a second embodiment of the substrate 100.

In this second embodiment, in addition to the layers 102, 104, 106 and108 described above with reference to the first embodiment, thesubstrate 100 comprises a heat absorption layer 120 located between thetrap rich layer 108 and the support layer 102. The material in layer 120is chosen such that it is sensitive to the wavelength of the laser usedto recrystallize the material in the first regions 110. The layer 120 isin thermal contact with layer 108. Furthermore, the layer 120 ispreferably very electrically insulating, or at least semiconducting withreduced electronic mobility to avoid adding electrical conductivityunder the layer 106. The layer 120 is also compatible withmicroelectronics front end processes that will be used to makecomponents on the substrate 100. Finally, the layer 120 is thick enoughto capture the thermal energy necessary for recrystallization of thematerial of layer 108, for example between about 30 nm and 3 μm.

Advantageously, the layer 108 comprises polycrystalline silicon, and thelayer 120 comprises polycrystalline germanium or polycrystalline SiGe ora phase change material.

In this second embodiment, the thermal absorption and electric chargetrapping functions are dissociated and distributed on the two layers 108and 120. Thus, the material in layer 108 can be chosen for its excellentcharge trapping properties without it necessarily being very absorbentrelative to the radiation used for recrystallization, and the materialof layer 120 is chosen to be very sensitive to heating. This secondembodiment enables to optimise the annealing effect of the laser byincreasing the absorption of laser radiation.

As a variant, the layer 120 may correspond to a stack of several layers.

FIG. 4 shows a third embodiment of the substrate 100.

In this third embodiment, the substrate 100 comprises a buffer layer 122in addition to layers 102, 104, 106, 108 and 120 described above. Thisbuffer layer 122 can limit or otherwise amplify recrystallization of thematerial in layer 108. For example, this buffer layer 122 comprises asemiconductor oxide or nitride. This layer 122 can be made as describedin document FR 2 973 158. It is also possible that the buffer layer 122is used in the substrate 100 without the thermal layer 120.

Regardless of the embodiment of the substrate 100, this substrate 100will be used to make a semiconducting device 200 comprising FDSOIcomponents and passive and/or RF components.

A method of making such a device 200 from the substrate 100 is describedbelow with reference to FIGS. 5A to 5D. The substrate 100 used in thismethod corresponds to the substrate 100 according to the firstembodiment described above. However as a variant, it is possible to usethe substrate according to one of the other embodiments described above.

When the substrate 100 comprises several first regions 110 and/orseveral second regions 112, the steps described below can be used forseveral or for each of the first regions 110 and/or the second regions112.

As shown on FIG. 5A, first insulating trenches 202 are made through thesurface layer 104, the buried dielectric layer 106 and the trap richlayer 108. These first trenches 202 electrically separate the firstregion 110 from the second region 112, within the trap rich layer 108.

One or several second insulation trenches 204 are also made throughlayers 104, 106 and 108 so as to electrically isolate a first part 206from a second part 208 of the first region 110, within the first region110 through which this or these second trenches 204 pass.

An implantation of dopants is then carried out in a portion 210 of thelayer 102 that is located in contact with the first region 110 of thelayer 108, and underneath this layer. On FIG. 5B, the dopantimplantation beams are symbolically represented by arrows with reference212. The portion 210 of semiconductor on which this implantation ofdopants was carried out forms a doped well electrically connecting thefirst and the second parts 206, 208 of the first region 110 to eachother.

FDSOI type components 214, particularly FDSOI transistors, are made in afirst portion of the surface layer 104 that is superposed on the firstregion 110 of the layer 108, and particularly in a first portion 216 ofthe surface layer that is superposed on the first part 206 of the firstregion 110 and that is well adapted to the fabrication of FDSOIcomponents due to the previous recrystallization of the first region110. These components 214 are connected to electrical interconnectionlevels formed within the intermetal dielectric layers 218 (FIG. 5C).

At least one electrical contact 219 is made through parts of the layers104 and 106 that are located above the second part 208 of the firstregion 110. This electrical contact 219 enables electrical access to thefirst part 206 of the first region 110, through the doped portion 210and the second part 208 of the first region 110, and applies the desiredelectrical potential onto this first part 206 of the first region 110that forms a back polarisation plane of the FDSOI transistors 214.

Finally, as shown on FIG. 5D, passive and/or RF components 220 are madeon and/or in a second portion 222 of the surface layer 104 located abovethe second region 112 forming an RFSOI part of the substrate 100. OnFIG. 5D, these components 220 correspond to a back-end inductor or to RFlines made above the part of the intermetal dielectric layers 218located on the second portion 222.

In the method described above with relation to FIGS. 5A-5D, the materialin the first regions 110 is recrystallized before the differentcomponents are made on the substrate 100. As a variant, thisrecrystallization can be done after the different components have beenfabricated on the substrate 100. In this case, recrystallization is donefrom the back face of the substrate 100, in other words using one ormore laser beams passing through the back face of the layer 102, so asnot to damage components already in place on the front face of thesubstrate 100.

The invention claimed is:
 1. A method of fabricating a semiconductor oninsulator type substrate, including fabrication of a stack comprising: asupport layer; a semiconductor surface layer; a buried dielectric layerlocated between the support layer and the semiconductor surface layer; atrap rich layer located between the buried dielectric layer and thesupport layer, and comprising at least one polycrystalline semiconductormaterial and/or a phase change material; and also comprising the making,in the trap rich layer, of at least one first region and of at least onesecond region adjacent to each other in the plane of the trap richlayer, during which the material in the at least one first region is atleast partially recrystallized such that its electrical resistivity isless than that of the material in the at least one second region.
 2. Themethod according to claim 1, in which fabrication of the at least onefirst region includes the implementation of local annealing of thematerial in the at least one first region, by laser.
 3. The methodaccording to claim 2, in which the semiconductor surface layer of thesemiconductor on insulator type substrate comprises monocrystallinesilicon and in which, during the local laser annealing of the materialof the at least one first region, the laser is focused on the at leastone first region of the trap rich layer through the semiconductorsurface layer and the buried dielectric layer of the semiconductor oninsulator type substrate.
 4. The method according to claim 2, in which,during local laser annealing of the material of the at least one firstregion, the laser is focused on the at least one first region of thetrap rich layer through at least the support layer of the semiconductoron insulator type substrate.
 5. The method according to claim 4, inwhich the semiconductor on insulator type substrate also comprises aheat absorption layer arranged between the trap rich layer and thesupport layer, and in which the laser is focused on a region of the heatabsorption layer superposed on the at least one first region of the traprich layer and through at least the support layer of the semiconductoron insulator type substrate.
 6. A method of fabrication of asemiconductor device, comprising at least: the implementation of themethod of fabrication of the semiconductor on insulator type substrateaccording to claim 1; fabrication of at least one first insulationtrench between the at least one first region and the at least one secondregion of the trap rich layer of the semiconductor on insulator typesubstrate, passing through at least the semiconductor surface layer, theburied dielectric layer and the trap rich layer of the semiconductor oninsulator type substrate; fabrication of at least one FDSOI component ina first portion of the semiconductor surface layer of the semiconductoron insulator type substrate that is superposed on the at least one firstregion of the trap rich layer of the semiconductor on insulator typesubstrate; and fabrication of at least one passive and/or RF componentin and/or on a second portion of the semiconductor surface layer of thesemiconductor on insulator type substrate that is superposed on the atleast one second region of the trap rich layer of the semiconductor oninsulator type substrate.
 7. The method according to claim 6, alsocomprising: fabrication of a second insulation trench passing through atleast the semiconductor surface layer, the buried dielectric layer andthe trap rich layer of the semiconductor on insulator type substrate,and separating first and second parts of the at least one first regionof the trap rich layer of the semiconductor on insulator type substrate;implantation of dopants in a portion of the support layer of thesemiconductor on insulator type substrate that is located in contactwith the at least one first region of the trap rich layer of thesemiconductor on insulator type substrate, forming a doped wellelectrically connecting the first and second parts of the at least onefirst region of the trap rich layer of the semiconductor on insulatortype substrate to each other; and fabrication of an electrical contactpassing through the semiconductor surface layer and the burieddielectric layer, in contact with the second part of the at least onefirst region of the trap rich layer of the substrate, allowing controlof a back polarisation plane of the FDSOI component formed by the firstpart of the at least one first region of the trap rich layer of thesemiconductor on insulator type substrate.